This invention relates to new and useful improvements in solutions containing sodium dehydroacetate with or without sodium borate decahydrate and/or disodium edetate.
The solutions are used as blood diluents for blood cell counting and sizing, and for use in hematological enumeration of blood cells and the determination of hemoglobin concentration by electronic particle analysis using a Coulter hemoglobinometer or similar automated cell (particle) counter.
The sodium azide acts as a preservative without altering the characteristics of the diluent in any way, but unfortunately it has certain undesirable features which are eliminated by the present invention.
One undesirable feature in the use of sodium azide as the effective bacteriostatic agent, is that it is relatively highly toxic so that aqueous solutions of sodium azide and vapours of hydrozoic acid can possibly contribute to adverse effects on laboratory workers if exposed to same. Furthermore, in the case of plumbing systems using copper and lead pipes and joints through which such solutions must be drained, it is necessary to exercise careful flushing procedures in order to prevent excess accumulations of heavy metal azides over extended periods of time, such excess accumulations sometimes leading to the formation of explosive conditions.
An attempt has been made to substitute other preservatives for sodium azide and an example of this is shown in U.S. Pat. No. 3,962,125 which uses, as a bacteriostatic agent, 2-phenoxyethanol. This agent is substantially less toxic than sodium azide and therefore eliminates the problems enumerated above. Unfortunately, however, it is necessary to use a percentage of sodium fluoride in such solutions containing 2-phenoxyethanol and the use of sodium fluoride has been found to have an etching effect on glass and related substances and therefore causes early deterioration of glass tubes and connections in scientific equipment, requiring frequent replacement of parts at considerable cost to the user.
Furthermore, sodium fluoride is classified as a very toxic substance (toxicity level 4-5 on a maximum scale of 6) see Clinical Toxicology of Commercial Products, Gosselin et al, editors, The Williams and Wilkins Company, Baltimore Fourth Edition, 1976, page 78. Indeed, 0.25-0.45 grams of sodium fluoride will cause severe toxic symptoms including nausea, vomiting, abdominal distress, diarrhea, stupor and weakness. Doses of only 4.0 grams will cause death. In this context, it is to be noted that sodium fluoride is being used as an insecticide for roaches and ants and in other pesticide formulations. (Martindale, The Extra Pharmacopoeia 27th edition, The Pharmaceutical Press, London, 1977, page 618; also see Clinical Toxicology of Commercial Products, above). It should be noted also that the long term genetic and cancer causing effects of all insecticides are currently under suspicion and review. Indeed, fluorides have been implicated specifically as carcinogenic agents.
In invention U.S. Pat. No. 3,962,125 sodium fluoride is said to be required to aid the conversion of hemoglobin to cyanmethemoglobin but the following also should be noted: (1) sodium fluoride is known as an excellent preservative of blood (Med J. Aust. 1:1939, 1968) and (2) Phenoxyethanol, the substance listed as the preservative in U.S. Pat. No. 3,962,125, is a rather poor preservative in its own right and is more effective when used in conjunction with other preservatives, such as the hydroxybenzoates (The Extra Pharmacopoeia, ibid page 1281). Similar co-operative effects can be expected for other preservatives such as fluorides but have, to my knowledge, not been specifically investigated.
It should be noted also that phenoxyethanol is a rather weak antimicrobial agent, being most effective against Pseudomonas aeruginosa, but less effective against proteus vulgaris, other gram negative organisms and gram positive organisms, even when used in concentrations 3 times as great as those of invention U.S. Pat. No. 3,962,125 (The listed concentration of 3.3 grams/liter is equivalent to a 0.33% solution, considering that phenoxyethanol is a liquid with a weight per ml of 1.105; usually a 1% solution is considered optimal for preservative use) see The Extra Pharmacopoiea, ibid, page 1281. In addition, phenoxyethanol carries a toxicity rating of 4 on a maximum scale of 6. See Clinical Toxicology of Commercial Products, ibid, page 123, item 424.